Little is known about what causes cellulite. It involves fibrous connective cords that tether the skin to the underlying muscle, with the fat lying between. As fat cells accumulate, they push up against the skin, while the long, tough cords pull down. This creates an uneven surface or dimpling.
In addition, hormonal factors play a large role in the development of cellulite, and genetics determine skin structure, skin texture and body type. Other factors, such as weight and muscle tone affect whether you have cellulite, though even very fit people can have it.
Cellulite is much more common in women than in men. In fact, most women develop some cellulite after puberty. This is because women's fat is typically distributed in the thighs, hips and buttocks — common areas for cellulite. Cellulite is also more common with aging, when the skin loses elasticity.
Weight gain can make cellulite more noticeable, but some lean people have cellulite, as well. It tends to run in families, so genetics might play the biggest role in whether you develop cellulite. An inactive lifestyle also can increase your chances of having cellulite, as can pregnancy.
Cited from Mayo Clinic